Piston oil ring having land flanked by concave sidewalls

ABSTRACT

An oil control ring for a piston of an internal combustion engine has an annular body defining a central axis. The ring has a U-shaped cross-section formed of a centrally positioned web extending parallel to the axis and a pair of axially spaced rail portions integrally connected to the web. Each rail portion extends radially outwardly with respect to the web, and an extremity of each rail portion defines a land extending parallel to the axis and adapted to sealingly engage a cylinder wall. Each land defines a pair of spaced chamfered sidewalls. Each sidewall extends contiguously from each land to define a chamfered edge adjacent the land. Finally, each chamfered edge defines a concave annular sidewall. The result is a reduction of land surface area in contact with the cylinder walls of an engine to provide improved performance, particularly during the engine break-in period.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to piston rings employed in pistons ofinternal combustion engines, and more particularly to designenhancements of oil control piston rings employed in such pistons.

[0003] 2. Description of the Prior Art

[0004] Those skilled in the art will appreciate that the pistons ofinternal combustion engines in today's modern vehicles are generallyprovided with three sets of piston rings for minimizing, between thepistons and their associated cylinder bores, the leakage of combustiongases to the engine crankcase, or of oil vapors to the combustionchamber.

[0005] A compression ring is generally provided in an upper region of apiston and is one hundred percent dedicated to operate as a gas-sealingmedium, so as to prevent entry of combustion gases into the enginecrankcase. A so-called lower compression ring is generally provided in amedial region of the piston body, providing approximately forty percentof the noted gas sealing function and sixty percent of an oil scrappingfunction. The lower compression ring is generally effective to preventoil vapors from traveling up to the top of the piston head to create theclassic smoking tailpipe or “blue smoke” syndrome.

[0006] Finally, most modern pistons include a third piston ring called alower or “bottom” oil control ring designed one hundred percent foraggressive scrapping of oil, and that is particularly adapted to forcethe oil back into the crankcase. Normally the oil control ring is thebottom-most piston ring, and in many modern engines constitutes aU-shaped flexible multidimensional ring. Accordingly, the ring includesa medial web supporting two spaced rail portions integrally connected tothe web.

[0007] It will thus be appreciated that various piston rings aredesigned to address either or both of the noted functions of preventionof leakage of gas to the crankcase, or of oil to the piston head.Generally, as the rings wear during their continuous scrapping againstthe cylinder walls and associated rocking within piston ring grooves,issues of blow-by of gases into the crankcase, and oil leakage intocombustion chamber areas, become significant. Most rings incorporate aninitial tangential tension in their structures (as measured by a springband) against the cylinder walls. This initial force, however, tends todiminish during the useful life of the piston ring.

[0008] Although substantially improved over the past decade, pistonrings of modern engines remain deficient in various other respects aswell. For example, in spite of the valuable scrapper function performedby the bottom oil control ring, an improved oil ring compression controlagainst the cylinder walls during the engine break-in period forenhancing performance during said period would be quite desirable.

SUMMARY OF THE INVENTION

[0009] The present invention provides a mechanism for optimizing radialpressure of a piston oil control ring against the cylinder wall of acylinder bore during the break-in period of an engine. An oil controlring for a piston of an internal combustion engine has an annular bodydefining a central axis. The ring has a U-shaped cross-section formed ofa centrally positioned web extending parallel to the axis, and a pair ofaxially spaced rail portions integrally connected to the web. Each railportion extends radially outwardly with respect to the web, and anextremity of each rail portion defines a land extending parallel to theaxis and adapted to sealingly engage a cylinder wall.

[0010] Each land defines a pair of spaced concave annular sidewalls.Each sidewall extends contiguously from each land. The concave surfaceof each sidewall results in a reduction of land surface area in contactwith the cylinder walls of an engine at any point during the enginebreak-in period. An improved performance, particularly during the enginebreak-in period, is realized through lower oil consumption and increasedfuel economy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of a piston ring that incorporatesthe improved engine break-in oil control feature of the presentinvention.

[0012]FIG. 2 is an enlarged view along lines 2-2 of inset A of FIG. 1,revealing details of an interior portion of one presently preferredembodiment of the oil control piston ring of this invention.

[0013]FIG. 3 is a similar enlarged view along lines 3-3 of inset A ofFIG. 1, revealing details of an exterior portion of the same presentlypreferred embodiment of the oil control piston ring of this invention.

[0014]FIG. 4 is a cross-sectional view of the oil control piston ring ofFIG. 1 along lines 4-4 of FIG. 1.

[0015]FIG. 5 is an enlarged fragmentary view of one rail portion of theU-shaped piston ring depicted in FIG. 4, highlighting the differencebetween a straight chamfered sidewall (shown in phantom) and the concavesidewall of the present invention.

[0016]FIG. 6 is a cross-sectional view similar to the view of FIG. 4 ofthe oil control piston ring, but including a coil spring used tofacilitate handling of the piston ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring initially to FIGS. 1, 2, and 3, the present inventionprovides an improved compression mechanism for a piston oil controlring. The mechanism is designed to optimize radial pressure of an enginepiston ring juxtapositioned against an associated engine cylinder borewall (not shown), particularly during the break-in period of an internalcombustion engine (not shown). Thus, an annular piston oil control ring2 is adapted to be used as a bottom scraper ring of a piston utilized inthe engine. The oil control ring 2 includes a circumferentially arrangedplurality of vertically slotted openings 4 (in the orientationdisplayed) that define vertically extending web segments 6. The segments6 are oriented parallel to a centrally positioned, vertically orientedaxis “a-a” of the control ring 2, depicted in FIG. 1.

[0018] Referring now particularly to FIGS. 2 and 3, a plurality ofsegmented rail portions 8 are integrally attached to the web segments 6in the “broken-ladder” style of FIG. 3. The rail portions 8 extendradially outwardly of the web segments 6, and are thus orthogonal to theaxis a-a. Collectively, the segmented rail portions 8 define radiallyextending gaps 9 between adjacent segments 8, as shown.

[0019] Those skilled in the art will appreciate that the slotted websegments 6 collectively form a substantially contiguous,circumferentially extending web portion 12, and that similarly thesegmented rail portions 8 collectively form contiguous upper and lowercircumferential rail portions 14 and 16, respectively. The web portion12 and the rail portions 14 and 16 are coupled together in thebroken-ladder arrangement so as to impart a high degree of flexibilityto the respective piston ring parts in the cylinder bore environment inwhich they must satisfactorily operate.

[0020] Referring now to FIG. 4, a U-shaped cross-section 10 of thepiston ring 2 displays in greater detail the connective relationshipsand orientation between the web portion 12, and the rail portions 14 and16 that extend radially outwardly of the axis aa (of FIG. 1). Theextremities of the rail portions 14 and 16 are defined by a pair oflands 18, 20 that are oriented parallel to the axis a-a, and aredesigned to directly engage and scrape the cylinder bore walls in areciprocal manner, as the piston containing the oil control ring 2reciprocates back and forth within a cylinder bore.

[0021] Each land 18, 20 is flanked by an inner concave chamferedsidewall edge 22 and an outer concave chamfered sidewall edge 24, asshown. Those skilled in the art will appreciate that each land 18, 20provides a cylinder wall contact surface area that is ideally maintainedso as not to become enlarged due to wear, particularly during thebreak-in period of an engine in which the oil control ring 2 is beingutilized. Indeed, in order to maximize contact pressure between theso-called “knife edge” land surface of the piston oil control ring, theconcave nature of the chamfered sidewall edges 22, 24 provides amechanism by which the land surface area stays smaller particularlyduring the break-in period, than any land area of the prior art.

[0022] Referring now to FIG. 5, those skilled in the art will appreciatethat the axial width dimension W of the lands 18, 20 should ideally bemaintained as short as feasible in order to minimize the contact areaduring break-in; prior art straight angled chamfered sidewall edges 40,46 are shown in phantom (via dotted lines) for comparison. During thebreak-in period, as wear occurs radially inwardly or along the “y” axisin the direction of the arrow shown, the worn width W′ of the land 20 isrepresentatively shown in phantom as land 42 after a first amount ofwear has occurred in the straight chamfered prior art sidewall edges 40,46. It will be apparent that the width W′ of the land 42 will havebecome substantially wider after said first amount of wear, thuscommensurately and undesirably increasing surface area in the straightangled chamfered sidewall edge. Indeed, the additionally increased widthW″ of the land 44 (shown in phantom) represents a second or more extremeamount of wear along the radial direction of the “y” axis, anddemonstrates that the width W″ becomes objectionably even greater.

[0023] Thus, those skilled in the art will appreciate that use ofconcave chamfered sidewall edges 22, 24 will provide a mechanism bywhich the land surface area stays smaller than otherwise possible, asdemonstrated in FIG. 5.

[0024] Finally, with particular reference to FIG. 6, a spring 30,preferably of the coil spring variety, is employed for handling anotherwise relatively flimsy annular oil control piston ring 2 of thepresent invention. The spring 30 imparts a relative rigidity tofacilitate the handling and installation of the piston ring 2 into apiston during assembly of engine parts. To the extent that the pistonring 2 operates in an oily environment, both the ring 2 and the spring30 may be made of a relatively inexpensive metal, such as carbon steel.

[0025] The above description is intended to be illustrative and notlimiting. Therefore, the scope of the invention should be determined,however, not with reference to the above description, but with referenceto the appended claims along with the full scope of equivalents to whichsuch claims may be entitled.

What is claimed is:
 1. An oil control ring for a piston of an internalcombustion engine, said ring comprising an annular body defining acentral axis, said ring having a U-shaped cross-section comprising acentrally positioned web extending parallel to said axis and a pair ofaxially spaced rail portions integrally coupled to said web, whereineach rail portion extends radially outwardly with respect to said web,an extremity of each rail portion defining a land extending parallel tosaid axis and adapted to sealingly engage a cylinder wall, each landdefining a pair of spaced angled sidewalls, each extending from eachsaid land to define a chamfered edge contiguously adjacent said land,wherein each said chamfered edge comprises a concave annular sidewall.2. The oil control ring of claim 1 wherein said concave annular sidewallcomprises an annular groove about the body of said ring.
 3. The oilcontrol ring of claim 2 wherein said web comprises a plurality of spacedweb segments that define apertures for the flow of oil from the cylinderwalls to piston oil return bores.
 4. The oil control ring of claim 3wherein said apertures are slotted, and wherein said slotted aperturesare regularly spaced about said annular body of said piston ring, andwherein each of said slotted apertures extends into each rail at an edgeof said rail.
 5. The oil control ring of claim 4 wherein said websegments are circumferentially spaced about said annular body, andwherein each web segments extends parallel to said axis.
 6. The oilcontrol ring of claim 5 wherein said oil control ring provides a reducedland contact dimension to minimize oil consumption during the break-inperiod of an engine.
 7. The oil control ring of claim 6 wherein saidring is a bottom scraper ring of a piston.
 8. The oil control ring ofclaim 7 wherein said ring comprises a carbon steel material.
 9. An oilcontrol ring for a piston of an internal combustion engine, said ringcomprising an annular body defining a central axis, said ring having aU-shaped cross-section comprising a centrally positioned web extendingparallel to said axis and a pair of axially spaced rail portionsintegrally coupled to said web, wherein each rail portion extendsradially outwardly with respect to said web, an extremity of each railportion defining a land extending parallel to said axis and adapted tosealingly engage a cylinder wall, each land defining a pair of spacedangled sidewalls, each extending from each said land to define achamfered edge contiguously adjacent said land, wherein each saidchamfered edge comprises a concave annular sidewall, wherein said ringfurther comprises an annular spring disposed between said rail portionsto impart rigidity to the ring, and to thereby facilitate handling ofsaid control ring.
 10. The oil control ring of claim 9 wherein saidannular spring is a coil spring.
 11. An oil control ring for a piston ofan internal combustion engine, said ring comprising an annular bodydefining a central axis, said ring having a U-shaped cross-sectioncomprising a centrally positioned web extending parallel to said axisand a pair of axially spaced rail portions integrally coupled to saidweb, wherein each rail portion extends radially outwardly with respectto said web, an extremity of each rail portion defining a land extendingparallel to said axis and adapted to sealingly engage a cylinder wall,each land defining a pair of spaced angled sidewalls, each extendingfrom each said land to define a chamfered edge contiguously adjacentsaid land, wherein said chamfered edge comprises a concave annularsidewall, wherein said concave annular sidewall comprises an annulargroove flanking said land about the body of said ring, and wherein saidring further comprises an annular spring disposed within said ring, saidspring situated between said rail portions and immediately adjacent saidweb.
 12. The oil control ring of claim 11 wherein each of said ring andsaid annular spring disposed within said ring comprises a carbon steelmaterial.